A magnetic random access memory (MRAM) is one of resistance random access memories. Writing methods of the MRAM include a magnetic-field writing method and a spin-injection writing method. Among these, the spin-injection writing method is advantageous in increasing the integration degree, reducing the power consumption, and enhancing the performance because it is characterized such that a spin injection current required for magnetization reversal becomes lower when a magnetic body has a smaller size. Furthermore, while erroneous writing to unselected memory cells may occur in the magnetic-field writing method due to spread of a magnetic field, such erroneous writing to unselected memory cells does not occur in the spin-injection writing method.
However, a read current in the spin-injection writing method is microscopic. To quickly sense a difference in these microscopic currents, sizes (current driving capabilities) of transistors included in sense amplifiers need to be increased to reduce performance fluctuations in differential amplification of the sense amplifiers. When the sizes of the transistors are increased, this results in increase in the sizes of the sense amplifiers themselves. Consequently, when the MRAM is further downscaled, it becomes difficult to arrange the sense amplifier with respect to each bit line pair. Therefore, when the MRAM is further downscaled, the sense amplifier is shared by plural bit line pairs. That is, the number of data (page size) that can be written or read in one access is reduced. Accordingly, the conventional MRAM using the spin-injection writing method adversely has a lower write or read speed than a DRAM, for example. Furthermore, the write time is longer than the read time in the MRAM. Because of this, a low data write speed has been a problem in the MRAM.